The present invention relates generally to a light guide for transmitting and/or distributing light. More particularly, the present invention relates to an internal extractor for a light guide that transports light by total internal reflection.
Light guides (i.e., light pipes, light conduits or light tubes) are commonly used to transmit light from a light source (e.g., a high intensity bulb) to a remote location with relatively low transmission losses. Light guides can also be used to effectively distribute decorative or functional light over relatively large areas.
Prism light guides and light guide luminaires are known in the patented prior art. The Whitehead U.S. Pat. No. 4,260,220, for example, discloses a hollow longitudinal light guide structure made of transparent dielectric material, such as acrylic plastic or optically clear glass, for transmitting or xe2x80x9cpipingxe2x80x9d light from a central source to a remote location. The light guide includes substantially planar inner and outer surfaces that are in xe2x80x9coctature.xe2x80x9d The light guide is formed of one or more longitudinal sections, each preferably having a constant cross-section along its length. The light guide can have a hollow rectangular or square cross-sectional structure made of four longitudinal wall sections bonded to form corners. The light guide can include an outer jacket or cover to protect the outer surface of the dielectric material from damage. The corners of the light guide are held in the protective jacket by corner strips and strip springs.
The Whitehead U.S. Pat. No. 4,615,579 discloses a luminaire for a prism light guide system including a light release mechanism for releasing light along the length of the light guide. The light release mechanism can be a non-planar surface, a rough outer surface, or round corners in an outer corrugated surface. The Whitehead U.S. Pat. No. 4,787,708 discloses a variety of additional techniques for continuously controlling the emission of light from a light guide such that, for example, the amount of light escaping per unit length along the light guide can be made constant to provide uniform illumination. To reflect any escaping light back into the luminaire so that it can be released through the desired surface, all of the outer surfaces through which it is not desired to have light escape can be covered by a highly reflective diffuse material such as a mirror, white paint, white plastic, white paper, or white fabric.
Light guides and light guide luminaires may be constructed with a variety of cross-sectional shapes as disclosed in U.S. Pat. Nos. 4,260,220 (Whitehead), 5,661,839 (Whitehead), 5,715,347 (Whitehead), and 4,805,984 (Cobb, Jr.). In addition, light guides can be constructed using a variety of materials such as transparent dielectric materials including acrylic plastic or optically clear glass as disclosed in U.S. Pat. No. 4,260,220 (Whitehead), or multi-layer optical films as disclosed in U.S. Pat. No. 5,661,839 (Whitehead).
The optical lighting film (hereinafter xe2x80x9cOLFxe2x80x9d) is typically a relatively thin sheet of transparent material (e.g., acrylic or polycarbonate) having a linear array of prisms embossed or otherwise formed at one side of the sheet. OLF""s suitable for use in manufacturing light guides are disclosed in U.S. Pat. Nos. 4,906,070 and 5,056,892.
Conventional light guide luminaire systems are typically constructed to a desired length and may be made in separate sections for handling and shipping ease. More recently, modular light guide luminaire systems have been developed utilizing a number of separate modules which are joined to form a chain as described in U.S. Pat. No. 5,901,266 (Whitehead). Each module is the same except for the extractor that must be sized to ensure the proper amount of light is emitted from each module depending on the location of the module within the chain. Since each module is constructed before it is assembled into a light distribution chain, a large inventory of modules, each having a specifically sized extractor, must be maintained to construct a light distribution system. Thus, current light guide luminaire systems must be designed for their intended end use application and once assembled, cannot be easily modified.
Various techniques have been used to extract light from a light guide for the purpose of illuminating an area. One technique involves altering the prisms (e.g., by rounding the prism corners, abrading the prisms, completely removing selected prisms, etc.) such that light is released through the altered regions. Another technique involves placing a light extractor on an inner surface of the light guide. Typically, the extractor is a strip or sheet of material (e.g., xe2x80x9cSCOTCH-CAL EXTRACTOR FILM(trademark)xe2x80x9d) configured to reflect the light toward the light guide wall at an angle outside the angular range of total internal reflection. When the light is reflected in such a manner, the internal reflectance of the light guide is reduced, thereby allowing light to escape through the wall of the guide to provide decorative or is functional lighting.
Some light pipe fixtures are designed to deliver the majority of the luminous flux upwardly, to reflect off the ceiling and down into the workspace. Diffuse lighting is highly desirable in certain applications where glare is a consideration, such as office space with computer screens. By locating a back reflector at the bottom of the light pipe, most of the luminous flux will be directed upwardly, leaving the back reflector with a soft glow. Locating the extractor along the top surface of the light guide will interfere with upward scattering of the luminous flux, thereby defeating the attempt to create indirect lighting. Locating the extractor along the bottom of the light guide will create a shadow on the back reflector.
It would therefore be desirable to provide an extractor for indirect lighting applications that does not create shadows on the light guide luminaire. It would also be desirable to create a light guide luminaire that can be easily modified or customized to meet particular end use applications, thereby reducing the inventory of modules needed to construct different light guide luminaire systems, and eliminating the need to separately design each segment of the light guide luminaire system based on the end-use application.
The present invention relates generally to an illumination device for transmitting and/or distributing light with an extractor that extends distally into the interior of the light guide.
In one embodiment, the illumination device comprises a hollow light guide including a wall having an inner surface and a structured outer side. The structured outer side includes a plurality of prisms defining grooves that extend along a length of the light guide. An extractor extends substantially along the length of the light guide and projects distally from the inner surface towards an interior of the light guide. The extractor is operative to cause light to be released through the wall of the light guide.
In one embodiment, the extractor comprises at least one treated surface operative to cause light to be released through the wall of the light guide. The treated surface can be a diffusely reflective surface. Alternatively, the treated surface comprises material removed from, and/or added to, at least a portion of a surface of the extractor. In another embodiment, the treated surface is a film applied to at least a portion of the extractor. The film may have diffusely reflective properties on one surface and an adhesive on the other surface. In yet another embodiment, the treated surface may be a printed pattern on at least a portion of the extractor. The printed pattern may be formed using inks, dyes or paints.
The extractor may progressively increase the quantity of light released through the wall of the light guide. The extractor may be a translucent material. In another embodiment, the extractor comprises a transparent material with one or more treated surfaces. The extractor may have a non-uniform surface area, either alone or in combination with the various treated surfaces.
The extractor can be shaped to generally follow a portion of a contour of the inner surface. The extractor can be permanently or releasably attached to the light guide. In one embodiment, the light guide comprises a mounting surface to which the extractor is attached. In another embodiment, an extrusion extends along the length of the light guide. The extrusion comprises an interface to which the extractor is attached. The extractor may be releasably attached to the extrusion.
The principles of the present invention also include a method of forming an illumination device comprising providing a hollow light guide including a wall having an inner surface and a structured outer side. An extractor is attached substantially along the length of the light guide and projects distally from the inner surface towards an interior of the light guide.
The principles of the present invention also include a method of forming an illumination device with a plurality of hollow light guides. An extractor is attached substantially along the length of the light guides and projects distally from the inner surface towards an interior of the light guides. The plurality of light guides are preferably substantially identical, while the extractor is designed for a particular installation site. In one embodiment, the plurality of light guides are attached together before the extractor is attached. In another embodiment, the plurality of light guides are installed at an installation site before the extractor is attached.